It's a good refreshment of Doom 3 packed in a shorter game, but with improved combat experience!
So there you have a "new" story about the old stuff: once again marines land to Mars after 2 years of "absence" from the previous events to collect data. This time, again as a marine, you get dragged into the battle immediately after the game starts, and that is something done right - you really don't need another introduction and feeling out process, because you know everything from the previous game. What you want is immediate action and you want this action to feel new.
So the key additions to improve the combat action are the new guns, monsters and combat style. Whether you might think, that this is a rip of from another game or not, you now get a gravity gun, just like the one in Half-Life 2. Doom 3 makes the weapon very versatile in combat situations, in fact so, that it stands it's own ground and feels more sited for combat than the one in Half-Life 2. This weapon makes you think and rewards the crafty. One weapon you really missed from previous Doom games was the double barrel shotgun - it makes it's return and feels awesome in the way it looks, sounds and does damage. With this weapon you adapt a new style of fighting - strafe fast towards a monster, shoot him down close, and then retreat fast for a reload!
The most impressive addition is the "revamped" soul cube. This time the soul cube has the ability to be upgraded - after finishing each of the bosses, your soul cube gets new powers, those you can use all the way through the game. This a is total uber upgrade, the key element of Resurrection Of Evil - by gaining the soul cube upgrades, you become more powerful in many ways, and so the game tosses more monsters and harder situations to counter it, and that is the best part about this Doom 3 add-on - the game just becomes more brutal, dynamic and challenging. By contrast, in this add-on there are far less quests and secondary objectives here, and you will not waste so much time by reading PDA letters and wondering around for hours and hours.. New monsters are present also, as well as bosses, but the most impressive one is the final boss - doctor Betruger himself! Of course it's not because he is super powerful, but rather due to the fact that he transforms from a charismatic bastard into a monstrosity.. Graphics and sound are just as good as in the original and game physics actually has been improved in some minor ways. One of the examples - the armor shards react to weave blasts and "scuttle" around..
The game is shorter than original and does not bring that feeling of awesomeness like the first time, but it's new icons and add-on + the improved combat style makes it a worthy successor.